How it works
Half base times height counts unit squares in the triangle. Heron computes from sides only when height is not given, using semiperimeter s.
Formula
A = ½ × base × height; Heron: A = √(s(s−a)(s−b)(s−c)), s = semiperimeter
How to use Area of a Triangle Calculator
- Choose base/height mode or three-side mode.
- Enter measurements in consistent units.
- Calculate and read square-unit area.
- For right triangles, either leg can be base with the other as height.
Worked examples
Concrete numbers and cases you can check against the tool above.
Base 10 m, height 6 m
A = ½×10×6 = 30 m² — height must be perpendicular to the 10 m base.
When to use Area of a Triangle Calculator
Roof gables, sail plots, and survey triangles often lack a drawn height. Heron’s formula saves an extra construction step.
Common use cases
- Area of a triangular garden plot.
- Geometry proofs checking Heron’s formula results.
- Graphics: UV triangle coverage in texture space.
Inputs and outputs
- Base and height
- Three side lengths (SSS)
Privacy
This tool runs entirely in your browser. Your data never leaves your device — nothing is uploaded to our servers.
Frequently asked questions
- Which side is the base?
- Any side — height must be perpendicular to that base, not necessarily another side length.
- Do three sides always form a triangle?
- They must satisfy triangle inequality; invalid triples should error.
- Right triangle shortcut?
- Area is ½ × leg₁ × leg₂ when legs are perpendicular.